Shaped detergent compositions, such as tablets are known in the art. These compositions hold several advantages over detergent compositions in particulate form such as ease of dosing, handling, transportation and storage. Consumers particularly like the convenience of dosing a shaped composition via the dispensing drawer.
Tablets are typically formed by compression of the various components. The tablets produced must be sufficiently robust to be able to withstand handling and transportation without sustaining damage. In addition, the tablets must also dissolve quickly so that the detergent components are released into the wash water as soon as possible at the beginning of the wash cycle.
Multi-phase detergent tablets have several advantages over single-phase tablets. Most notably multi-phase tablets allow essentially incompatible ingredients to be formulated in a single dosage unit. For example, it is desirable to formulate a single-dose composition that comprises both surfactant and fabric softener. However, many of the commonly used surfactants will form complexes with the fabric softener materials leading to poor cleaning, poor softening and, possibly, residues on the fabric. Therefore, any composition comprising both materials must either be formulated using a limited number of compatible materials or be designed to sequentially release said ingredients, thereby avoiding the problems of incompatibility. Multi-phase tablets described in the prior art are typically prepared by compressing a first composition in a tablet press to form a substantially planar first layer. A further detergent composition is then delivered to the tablet press on top of the first layer. This second composition is then compressed to form another substantially planar second layer. Thus the first layer is generally subjected to more than one compression as it is also compressed during the compression of the second composition. The Applicant has found that, because the compression force must be sufficient to bind the first and second compositions together, the resultant tablet has a slower rate of dissolution. Other multi-phase tablets exhibiting differential dissolution are prepared such that the second layer is compressed at a lower force than the first layer. However, although the dissolution rate of the second layer is improved, the second layer is soft in comparison to the first layer and is therefore vulnerable to damage caused by handling and transportation.
EP-A-481547 discloses a dishwashing detergent tablet which, it is alleged, can provide sequential release of a dishwashing composition and a rinse aid composition. The tablets of EP-A-481547 have an inner layer which is completely surrounded on all sides by a barrier layer which, in turn, is completely surrounded by an outer layer. WO-A-99/40171 discloses a detergent tablet for fabric washing where there is a fabric conditioning agent present in one zone of the tablet at a greater concentration than in another zone. It is claimed that the conditioning agent may be a softening agent in a zone or region which disintegrates later than another zone or region of the tablet. It is alleged that this delayed disintegration can be achieved through blocking access of water to the zone which is intended to disintegrate later or by adding disintegration enhancing materials to the zone which is intended to disintegrate first. WO-A-00/06683 discloses a tablet composition for use in the washing machine that has at least one particle that is made up of at least one nucleus comprising at least one substance that acts mainly during the rinsing process of the washing machine in addition to a coat that fully surrounds the nucleus and comprises at least one compound whose solubility increases when the concentration of a specific ion in the ambient medium is reduced. WO-A-00/04129 describes multi-phase detergent tablets where there is a first phase that is in the form of a shaped body having at least one mould therein and a second phase in the form of a particulate solid compressed within said mould. In preferred embodiments of the multi-phase tablets of WO-A-00/04129 the second phase (and any subsequent phases) dissolves before the first phase.
However, prior art tablets often do not effectively control of the delivery of the actives. Frequently, the active(s) are expelled from the wash before the rinse cycle along with the wash liquor from the main wash. This means they do not have a chance to release the active(s). In addition, when the actives are released early it can lead to essentially incompatible phases being released at the same time. Also, many of the actives work most effectively when released towards the end of the laundry cycle so they are not degraded or washed away by the wash liquor. Moreover, due to their chemical and physical properties, the prior art tablets often do not disintegrate quickly. This means it can be difficult to dose the tablets via the dispensing drawer and there is a risk of residues remaining on the clothes. Furthermore, when dispensed via the drawer the particle size of the disintegrated composition must be such that it can pass from the drawer, through the pipe and into the drum often through small holes.
It is an object of the present invention to provide a shaped detergent composition that can be formulated to delay the delivery of an active until the appropriate time in the laundry cycle. It is a further object of the present invention to provide a shaped detergent composition that is not only sufficiently robust to withstand handling and transportation, but is also convenient to dose via the dispensing drawer. Other objects and advantages shall become apparent as the description proceeds.